Can climate change cause earthquakes? We look at the science and the spin
- 11 Jun 2012, 12:30
- Carbon Brief staff
A new book suggesting a link between man-made climate change and
increased seismic events has got some stick. A look at the science
shows the theory isn't nearly as mad as it's made out to be - but
it doesn't necessarily merit the apocalyptic publicity spin.
When Professor Bill McGuire of University College London
introduced his new book
Waking the Giant: How a changing climate triggers earthquakes,
tsunamis, and volcanoes on the Guardian's science weekly
podcast a few weeks ago, he started with a warning: "It does
sound a bit mad, but it isn't..."
So do we face an age of "geological havoc" thanks to man-made
climate change, as
McGuire told his audience at the Hay literary festival last
week? Motor journalist and climate skeptic Jeremy Clarkson
doesn't buy it, labelling McGuire's theory "science fiction" in the
Sunday Times yesterday.
It's hard to see how anyone could invoke climate change and
earthquakes in the same sentence without getting some stick, and
Clarkson
isn't the only
person to treat the notion that a changing climate can affect
the ground beneath our feet with derision. But a closer look
suggests the theory not only makes sense, it also appears to have
historical precedent.
Waking the Giant
McGuire's book examines what the planet has done in the past as
the climate has changed naturally, and makes a convincing case for
a historical relationship between natural climate change and some
geological activity. Given the speedy nature of current climate
change, it seems reasonable to take from this that our current
human-driven climate change will have geological consequences -
indeed, Clarkson concedes that the "theory that global warming can
affect the fabric of the planet is based in fact".
However, some of the publicity around the book has prompted
headlines which ask if climate change might "
unleash geological mayhem". This seems quite unhelpful; after
all, one man's imminent geological mayhem might be another's
long-term rumble.
We had questions about exactly what kind of changes might occur,
and when. So we got in touch with McGuire and asked him if he could
give us a more precise view of what he thinks might happen.
The argument
First, though, the theory. The argument goes like this: when the
climate changed naturally in the past, and the planet emerged from
an ice age, large ice sheets covering much of the planet retreated.
They were so heavy that the resulting release of pressure on the
earth's crust caused it to 'bounce back', triggering
earthquakes, tremors, and even volcanic
activity along pre-existing fault lines.
Right now, the Earth is still responding to the end of the last
ice age some 20,000 years ago when temperatures began to rise,
causing large ice sheets to retreat, as shown here:
Rate of crustal bounce-back following the end of the last
ice age, as modelled by
Paulson et al. (2007). Source:
NASA.
McGuire suggests that if man-made climate change leads to more
large ice sheets disappearing - like the one covering Greenland -
this could lead to more shakes, rattles and rolls.
What's the scientific evidence?
It's worth noting here that although the historical relationship
between ice sheet retreat and geological change is
pretty well
documented,
research looking at more recent man-made climate change is rather
sparse. A 2009 meeting at University College London
concluded that, since climate change in the past has probably
increased some 'geological hazards';
"Anthropogenic climate change therefore
has the potential to alter the risk of geological and
geomorphological hazards through the twenty-first century and
beyond. Such changes in risk have not yet been systematically
assessed."
To us that does sound like an endorsement of the general theory.
But the last part says that the risks of dangerous
changes in the earth's surface due to man-made climate change
haven't yet been intensively investigated.
Roland Burgmann, a geologist at the University of California,
Berkeley, told
Live Science (in 2007) that changes in ice cover can affect the
earth's crust, but more research is needed to work out the scale of
the risk and where effects like earthquakes might happen.
What's the timeline?
It's also not very clear from the publicity around the book when
exactly we're supposed to be worried about any 'geological mayhem'
occurring. Are we talking in the next century, or the next
millennium?
When asked on the Guardian Science podcast whether his worries
about Greenland could materialise this century, McGuire says:
"Not by the end of this century, no
[...]."
But contrast this with a video promoting
the book, where McGuire says:
"[T]he worry is, that if we don't act
very soon, then the Earth is going to bite back with a real
vengeance over the next 70-100 years."
We put it to McGuire that this wasn't particularly clear. He
replied that, although the Greenland ice sheet is not going to
fully disappear by the end of the century (it would need to be kept
at a sufficiently warm temperature for a few
thousand years for that to happen), there is a
study suggesting that we could see more earthquakes in
Greenland in coming decades.
He also said that in Alaska "the response - in the way of
earthquake activity and giant landslide frequency - is already
apparent". Here he's probably referring to research like this paper
showing an increase in small earthquakes between 2002 and 2006,
thought to be down to ice loss.
Of the potential for volcanic activity triggered by climate
change he told us:
"[W]e don't have a handle on how quickly
we will see a response [...]. It may, however, be a while before we
can distinguish any elevated level of activity from the normal
background. In many ways, pinning down how quickly the solid Earth
will respond this time round is no easy task and has to be
speculative to some degree."
Essentially, this is the 'it's complicated' caveat so common in
scientific conclusions. But as you will have spotted, these
explanations are couched in considerably more careful language than
some of the publicity for the book.
Following the Hansen model?
There does seem to us to be a disparity between McGuire's
publicity for the book, with its emphasis on the most dramatic
possible outcomes from his hypothesis, and the more careful
statements he's made in scientific papers and outside the publicity
circuit.
In discussing temperature change this century in his book,
McGuire's predictions err towards the upper end of the scale, and
he also talks of facing sea level rise comparable to that at the
end of the last ice age, when sea level rose at an average of one
metre per century - within the
range of projected sea level rise for high-end scenarios of
temperature rise. In both this, and his tendency to talk in stark
language, McGuire seems to be borrowing a leaf from James Hansen's
book.
McGuire told us in an email:
"We are currently on a high-end
emissions scenario track and prospects for getting off this any
time soon look pretty bleak [...]. These scenarios are Met Office
Hadley Centre scenarios that build in carbon feedbacks, and are -
in my opinion - very realistic. In relation to sea level, the
consensus now is that a 1 - 2m rise is most likely by 2100."
McGuire is also clearly coming from a particular viewpoint:
"The language used in scientific papers
is always careful, but released from the constraints of
peer-reviewed journals we are able to express our thoughts in a
more personal manner - as James Hansen in the US has done so
effectively. My personal opinion is that climate change will be
catastrophic - even without any geological response."
Perhaps it's not that surprising that book authors will try and
make their work sound exciting. But there are no end of newspapers
willing to pounce on catastrophic visions of the future in order to
perpetuate the 'it's an apocalypse/it isn't happening' see-saw that
makes up the worst end of climate reporting.
McGuire is not shying away from discussing high-end scenarios,
which is fair enough. But in our view he should make clear that
this is what he is doing, and also more carefully communicate the
uncertainty in his work. After all, it appears to be decidedly
early days for this research.